Method and structure for producing bumps on an IC package substrate

ABSTRACT

A method and structure for producing bumps on an IC package substrate. The method first deposits a medium layer on a protective layer of the IC package substrate, which has good adherence ability to both the copper layer and the protective layer. Then, a CVD process is applied to deposit a copper layer on the medium layer to form the metal layer. A dry film is thereafter formed on the metal layer and several contact widows are opened therein. A metal pad and a bump are electroplated in the contact windows. Then remove the dry film, the bumps are protruded out of the substrate with a predetermined height to be solder bumps with an IC chip. By said method, an IC chip no longer needs to form bumps thereon anymore and to save cost and reduce pitch between bumps down to 150 μm. And package size is scaled for smaller IC chips and for smaller component dimension.

FIELD OF THE INVENTION

[0001] This invention relates to a novel method and structure forproducing bumps for IC package substrate, and more particularly to aFlip-Chip BGA substrate with solder bumps form thereon.

DESCRIPTION OF THE PRIOR ART

[0002] Nowadays, many companies are trying very hard to approach smallerand more effective IC chips technology of Integrated Circuit Chip. Inaddition to the improvements of IC chips, the IC Package Technology alsohas great achievement. From Lead Frame Package to BGA Package and toTape Automatic Bonding BGA, TAB BGA, kinds of IC Package technologiesare invented for IC chips, which are smaller and smaller again. To adaptfor advance technology, mini BGA and Chip Scale Package (CSP) arecreated for the scale of substrate/chip value less than 1.2. And to doso, most of them apply Flip-Chip technology to package these chips withpackage substrates.

[0003] Please refer to FIG. 1; a prior Flip-Chip technology is presentin it. The prior Flip-Chip technology first applies a BGA substrate 11and forms a circuit layer 12 and a protective layer 13 thereon. Severalcontact windows are opened to expose some portions of the circuit layer12. A solder pad 14, which is preferably made up by copper, tin and leadmaterials, is electroplated on the exposed circuit layer 12 in thecontact window and a bump 15 is thereafter formed on.

[0004] On active side of the IC chip 21, an Aluminum alloy layer 22 anda protective layer 23 are formed thereon. A solder bump 24 (or goldbump) is also formed on the IC chip 21, which is contacted with theAluminum alloy layer 22. During package, the IC chip 21 is heated andpressed onto the BGA substrate 11 to merge the solder bump 24 and thebump 15, by which not only electrically connects the IC chip 21 and theBGA substrate 11 and also binds themselves into one complement.

[0005] However, such a structure has some disadvantages as describedhereunder.

[0006] 1, the pitch between the bumps, which are made by screen printtechnology, are mostly around 200˜250 μm. By screen print technology orattaching BGA bumps onto the substrate, which are not very criticaltechniques, it is very difficult to make pitches less than 150 μm.

[0007] 2, the cost is higher to make bumps 24 on the IC chips 21. Thefacilities for producing IC are very expensive. In addition, theintegrated circuits, which are composed by light doped silicon, silicideand metal Aluminum, are very complicated and lower heat-resistant. Thebumps on the IC chip are no doubt made under critical conditions bycostly facilities. Thus, the cost is higher and the yield is lower. Onthe other side, circuits on the BGA substrate are made by copper, whichcan endure higher heat, and are much easier to make than those on ICchip. So, if bumps were made on the BGA substrate, those disadvantagescan be overcome.

SUMMARY OF THE INVENTION

[0008] The object of present invention is to form bumps on the Flip-ChipBGA substrates. This object no longer forms the bumps formed on IC chipsbut BGA substrates. The bumps on the BGA substrates can still work forIC chips soldering therefore to reduce cost.

[0009] The other object of present invention is to replace bump screenprint technique by metal electroplating to scale down the distancebetween bumps, even less than 150 μm. So the feature size of the packagedevice could be further minified.

[0010] Therefore, the embodiment of present invention for producingbumps on BGA substrate comprises the steps of:

[0011] A) Applying a substrate, on which a circuit layer in formedthereon. A protective layer is formed on the circuit layer and there areseveral contact windows opened therein to expose the circuit layer.

[0012] A1) Depositing a medium layer on the protective layer, which isalso opened at the contact windows.

[0013] B) Electroless metalizing a metal layer on the surface of thesubstrate, which covering the surface of the medium layer, the insidesurface of the contact window, and the surface of the exposed circuitlayer.

[0014] C) Forming a dry film on the metal layer, which is opened at thecontact windows to expose the metal layer.

[0015] D) Forming metal pads with a predetermined thickness on theexposed metal layer.

[0016] E) Forming bumps on the metal pads.

[0017] F) Removing the dry film and the metal layer thereon whichprotrudes the bumps out.

[0018] G) Reflowing and flatting the bumps to generalize them intostandard scale.

[0019] In this invention, protruded bumps are formed on the BGAsubstrate for soldering with an IC chip. Therefore, the IC chip nolonger needs to make bumps thereon. And the electroplating technique isused as a replacement of the screen print technique to scale thedistance between bumps down to 150 μm and around 80˜120 μm. Therefore,the improved BGA may be applied on to smaller IC chips to catch up thetrend.

[0020] The structure of this invention comprises a substrate, a circuitlayer made on the substrate, a protective layer on the circuit layerwith contact windows therein, a metal layer on the circuit layer, metalpads on the metal layer, and bumps on the metal pads for soldering withan IC chip.

[0021] However, some solder balls are also formed on the other side ofthe substrate for connecting with a motherboard. For connecting with amotherboard, the pitches of these solder balls are more than 200 μm,which have different purposes and producing method with presentinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] These and other features and advantages of the present inventionwill become more apparent from the following detailed description ofexemplary embodiments thereof as illustrated in the accompanyingdrawings, in which:

[0023]FIG. 1 is a perspective view of the prior Flip-Chip technology.

[0024]FIG. 2A˜2H is the steps of a method of the present invention tomake bumps on BGA substrate and structure thereof.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0025] Present invention is to form bumps on the Flip-Chip BGAsubstrates. The bumps are no longer formed on IC chips but BGAsubstrates. A medium layer is firstly made on a protective layer outsideof the substrate. The medium layer is made up by a material, which hasgood adherence ability to copper ions and the protective layer toovercome the issue that copper ions doesn't easily attach on theprotective layer. Thereafter, a metal layer (copper layer) is depositedon the substrate. A dry film is formed thereon and contact windows areopened. In the contact windows, a copper layer and bumps which made byStannum/lead alloy are formed in sequence. After removing the dry film,the bumps are protruded out of the substrate with a predetermined heightto be solder bumps with an IC chip.

[0026] Please refer to FIG. 2A˜2H, the steps of the embodiment.

[0027] Step 1: Please refer to FIG. 2A. A BGA substrate 31, on which acircuit layer 32 (with copper or gold material) and a protective layer33 on the circuit layer 32 are formed thereon, is firstly applied. Acontact window 34 is opened in the protective layer 33 to expose someparts of the circuit layer 32.

[0028] And on the other side of the BGA substrate 31, a second circuitlayer 52 is formed thereon. A conductive through hole 55 is made toconnect the circuit layer 32 and the second circuit layer 52. A secondprotective layer 53 and a second contact window 54 are also formed. Asolder ball 56 is formed in the second contact window 54, which isapplied to merge with motherboard or circuit board (not shown in FIG.2A). Because said conductive through hole 55, and the circuit layer 52on the lower surface of the substrate, the second protective layer 53,the second contact window 54, and the solder bump 56 are well-known andnot the feature of the present invention, so they aren't go intodetails.

[0029] Step 2: please refer to FIG. 2B. A medium layer 35 is made on theprotective layer 33 and also opened at the contact window 34. The mediumlayer 35 is deposited to resolve an issue that metal ions, such ascopper, may not able to attach on the protective layer 33. So, thematerials of the medium layer 35 have good adherence ability for themetal ions and the protective layer 33. The materials may be chromium,titanium and oxidized copper. This medium layer 35 may be formed bychemical vapor deposition (CVD) method, sputtering, printing, spincoating (only for liquid resin) or pasting a thin metal thin film anddefined by photo resister, photography, etching to open the medium layer35 for exposing the circuit layer 32.

[0030] Step 3: please refer to FIG. 2C. A metal layer 36 is formed onthe surface of the BGA substrate 31 by electroless metalizing, whichcovering the surface of the medium layer 35, the inside surface of thecontact window 34, and the surface of the exposed circuit layer 32. Thematerial of the metal layer 36 may be chromium, titanium, copper, gold,iron, or nickel. The metal layer 36 is deposited by sputtering orchemical deposition, which used in plating through hole (PTH)technology. The metal layer 36 works as a conducting circuit at thefollowing electroplating process, and is removed after saidelectroplating process, so it's no need to have a thick thickness. Andthe peel strength does not need to be high, either. Of course, a thickermetal layer may be form on the metal layer 36 if required.

[0031] Step 4: please refer to FIG. 2D. A dry film 37 with an opening atthe contact window 34 is formed on the metal layer 36 to expose themetal layer 36. The material of the dry film 37 may be polymer,photo-resister, and made by spin coating, printing or pasting. In theembodiment, the dry film 37 is made by photo-resister, which is definedby a photo mask to translate patterns thereon.

[0032] Step 5: please refer to FIG. 2E. A metal pad 38 is electroplatedon the metal layer 36. The material of the metal pad 38 may be chromium,titanium, copper, gold, iron, nickel, or alloy thereof. Generally, thethickness of the metal pad 38 is preferable a little bigger or equal tothe protective layer 33.

[0033] Step 6: please refer to FIG. 2F. A bump 39 is formed on the metalpad 38 by continuous electroplating. The material of the bump 39 may becopper, tin, lead or alloy thereof. In the embodiment, the thickness andthe position of the metal pad 38 and bump 39 are defined by the dry film37. However, two dry films may be applied to define the metal pad 38 andbump 39 in two steps independently in another preferred embodiment.

[0034] Step 7: please refer to FIG. 2G. The dry film 37, the mediumlayer 35 and the metal layer 36 on the protective layer 33 are removedaway. In the embodiment, selective dry etching technology is applied toremove them. However, if the medium layer 35 is pasted on the protectivelayer 33, all of them (the dry film 37, the medium layer 35 and themetal layer 36) can be peeled away easily. As described, the dry film37, the medium layer 36 and the metal layer 35 are removed at last, sothey don't need high attaching ability. The metal layer 36 is very thin,so even been peeled directly; the metal pad 38 and bump 39 will not behurt. (Because the attaching ability of electroplating is better.) Step8: please refer to FIG. 2H. Reflow and generalize the bumps 39 intobumps 391 to make each of them as high as a pre-determined value. Thebumps 391 are higher than the surface of the BGA substrate. So it candirectly merge with an IC chip. So, on the IC chip, there is no need tomake bumps anymore. In this invention, the bumps 391 are made byelectroplating which have higher accurate than prior technology.Therefore the pitch between bump balls may down to 150 μm and around80˜120 μm to fit the specification of the heat pressing process.

[0035] And on the other side of the BGA substrate 31, a second circuitlayer 52 is formed thereon. A conductive through hole 55 is made toconnect the circuit layer 32 and the second circuit layer 52. A secondprotective layer 53 and a second contact window 54 are also formed. Asolder bump 56 is formed in the second contact window 54, which isapplied to merge with motherboard (not shown in FIG. 2A).

[0036] From the above, the invention has the following advantages.

[0037] 1, The pitch between bumps is smaller than prior art. Byelectroplating, the bump has pitch between each other downed into 80˜120μm to fit the specification of the heat pressing process. Thereforesmaller IC chips are adapted by this invention.

[0038] 2, The bump has lower cost than prior art. The bump is made onthe BGA substrate by electroplating. Compared to the technology whichforming bumps on IC chip, the present invention is under a looserprocess condition and technical complexity, and have a higher yield andlow cost than prior art.

[0039] It's understood that the above-described embodiment is merelyillustrative of the possible specific embodiment, which may present mainprinciples of the invention. Other arrangements may readily by devisedin accordance with these principles by those skilled in art withoutdeparting from the scope and spirit of the invention.

What be claimed is
 1. A method for producing bumps on an IC packagesubstrate, comprising the steps of: A) applying a substrate, on which atleast a circuit layer in formed thereon, and a protective layer isformed on the circuit layer and a plurality of contact windows areopened therein to expose the circuit layer; B) electroless metalizing ametal layer on the surface of the substrate, which covering theprotective layer and the exposed circuit, layer; C) forming a dry filmon the metal layer, and positions in the dry film relative to thecontact windows are also opened to expose the metal layer; D) forming ametal pad with predetermined thickness on the exposed metal layer byelectroplating; E) forming a bump on the metal pad; F) removing the dryfilm and the metal layer thereon by which the bumps are protruded out:2. The method of claim 1, wherein between said step A and step B,comprises a step (A1): a medium layer is formed on the protective layerand opened at the contact window.
 3. The method of claim 2, wherein saidmaterial of the medium layer has good adherence ability to theprotective layer and the metal layer.
 4. The method of claim 2, whereinsaid the medium layer is made up by a technology choosing from a groupconsisting of CVD, electroplating, spin coating, screen printing, andpasting technologies.
 5. The method of claim 1, wherein between saidstep B and step C, comprises a step (B1): increase the thickness of themetal layer by electroplating.
 6. The method of claim 5, wherein saidthe increased material of step B1, is not the same with the metal layer.7. The method of claim 1, wherein said electroless metalizing a metallayer in step B is by sputtering or chemical deposition.
 8. The methodof claim 1, wherein said material of the protective layer is chosen froma group consisting of resin, polymer and photo-resister.
 9. The methodof claim 1, wherein said protective layer is made up by a technologyfrom a group consisting of spin coating, screen printing, and pastingtechnologies.
 10. The method of claim 1, wherein said dry film is formedand defined by the following steps: C1) forming a dry film on thesubstrate; C2) translating a pattern by a photo mask to the dry film;C3) defining the dry film by photography technology to expose the metallayer.
 11. The method of claim 1, wherein the material of said metal padis chosen from a group consisting of copper, gold, nickel, chromium,aluminum, and alloy thereof.
 12. The method of claim 1, wherein saidmaterial of the bump is chosen from a group consisting of copper, tin,lead and alloy thereof.
 13. The method of claim 1, wherein a step (G) isfurther applied after said step (F), which: reflows and flats the bumpto generalize it into standard scale.
 14. A structure of packagesubstrate which has bumps thereon, comprising: a substrate; a circuitlayer on the substrate; a protective layer covered on the circuit layerwith a contact window to expose the circuit layer; a metal layer coatedin the contact window and on the circuit layer; a metal pad formedinside the contact window and on the metal layer; a bump, formed on themetal pad which is protruded from the substrate.
 15. The structure ofclaim 14, wherein said material of the metal layer may be titanium,chromium, nickel, gold, copper, iron, chromium or alloy thereof.
 16. Thestructure of claim 14, wherein said material of the metal pad may becopper, gold, nickel, aluminum, chromium, or alloy thereof.
 17. Thestructure of claim 14, wherein said material of the bump is chosen froma group consisting of copper, lead, tin, and alloy thereof.